Fluorescent isoindoline dyes

ABSTRACT

The present invention provides a new class of excited state intramolecular charge transfer (ESIPT) dye compounds based on mono or dihydroxy substituted 1,3-bisiminoisoindole motif and metal complexes containing such compounds as ligands. The present invention also provides OLEDs containing the compound and/or metal complex as the emissive material.

REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/423,822, filed Dec. 16, 2010, the content of which is incorporatedherein by reference in its entirety.

RESEARCH AGREEMENTS

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, The University of Southern California, and theUniversal Display Corporation. The agreement was in effect on and beforethe date the claimed invention was made, and the claimed invention wasmade as a result of activities undertaken within the scope of theagreement.

FIELD OF THE INVENTION

The present invention relates to a new class of excited stateintramolecular charge transfer (ESIPT) dye compounds based on mono ordihydroxy substituted 1,3-bisiminoisoindole motif and metal complexescontaining such compounds as ligands. The present invention also relatesto uses of these compounds and/or metal complexes in organic lightemitting devices.

BACKGROUND OF THE INVENTION

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule istris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the structureof Formula I:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule”, and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

1,3-bis(2-pyridylimino)isoindoline (BPI) was originally synthesized in1952 in two steps, as described by Elvidge, J. A.; Linstead, R. P. J.Chem. Soc. 1952, 5000, and later one step as described by Clark, P. F.;Elvidge, J. A.; Linstead, R. P. J. Chem. Soc. 1953, 3593, both of whichare incorporated herein by reference. The production of gram scalequantities required harsh reaction conditions and as a result, producedmany side reactions including formation of phthalocyanine and relatedchromophoric by-products. It was not until the metal ion catalyzedreaction (Scheme 1) published by Siegl in 1977 (Siegl, W. O. J. Org.Chem. 1977, 42, 1872-1878, incorporated herein by reference) that theBPI ligand became a viable option for various applications. The BPIligand is interesting for many types of research because it is easy toprepare, is highly stable and can be easily modified to suit aparticular interest. Examples of this include Siegl's later work (seeSiegl, W. O. J. Heterocycl. Chem. 1981, 18, 1613) producing watersoluble derivatives; BPI derivatives capable of chelating two, e.g.,described in Siegl, W. O. Inorg. Chem. Acta 1977, 25, L65, or eventhree, e.g., described in Marks, D. N.; Siegl, W. O.; Gangne, R. R.Inorg. Chem. 1982, 21, 3140-3147, and Anderson, O. P.; la Cour, A. Dodd,A.; Garrett, A. D.; Wicholas, M. Inorg. Chem. 2003, 42, 1.22-127, metalions; and derivatives with extended conjugation, e.g., described inBaird, D. M.; Maehlmann, W. P.; Bereman, R. D.; Singh, P. J. Coord.Chem. 1997, 42, 107-126, all of which are incorporated herein byreference.

SUMMARY OF THE INVENTION

The present invention provides an excited state intramolecular chargetransfer (ESIPT) dye compound based on mono or dihydroxy substituted1,3-bisiminoisoindole motif and a metal complex containing such acompound as ligand.

In one embodiment, the present invention provides a compound of thefollowing formula:

wherein Y₁ and Y₃ are independently S, O, or NR₁, and S, O, or NR₃,respectively, with at least one of Y₁ and Y₃ being NR₁ and NR₃,respectively, R₁ and R₃ each being an atom or a functional group,wherein R₁ and R₃ can optionally form a ring; R₂ is an atom or afunctional group, wherein R₂ can optionally form a ring with Y₁ and/orform a ring with Y₃; and X₁, X₂, and X₃ are independently N or CR₄, N orCR₅, and N or CR₆, respectively, R₄, R₅, and R₆ each being an atom or afunctional group, wherein R₄ and R₅ and/or R₅ and R₆ can optionally forma ring or R₄ and R₆ can optionally form a ring.

In another embodiment, the present invention provides a complexcomprising a metal atom M and a ligand as shown by the followingformula:

wherein - - - - - represents an optional coordination bond, at least oneof which being present and wherein Y₁ and Y₃ are independently S, O, orNR₁, and S, O, or NR₃, respectively, with at least one of Y₁ and Y₃being NR₁ and NR₃, respectively, R₁ and R₃ each being an atom or afunctional group, at least one containing an atom for forming acoordination bond, wherein R₁ and R₃ can optionally form a ring; and X₁,X₂, and X₃ are independently N or CR₄, N or CR₅, and N or CR₆,respectively, R₄, R₅, and R₆ each being an atom or a functional group,wherein R₄ and R₅ and/or R₅ and R₆ can optionally form a ring or R₄ andR₆ can optionally form a ring. The metal M can be a transition metal ora lanthanide.

In yet another embodiment, the present invention provides an OLEDcomprising an organic layer disposed between an anode and a cathode,where the organic layer comprises the compound and/or the metal complexof the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows an ¹H NMR and ¹³C NMR spectra for1,3-bis(dodecylimino)-4,7-dihydroxyisoindole (1).

FIG. 4 shows an ¹H NMR spectra for1,3-bis(p-tert-butyl-phenylimino)-4,7-dihydroxyisoindole (2).

FIG. 5 shows an ¹H NMR and ¹³C NMR spectra for1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole (3).

FIG. 6 shows an ¹H NMR spectra for5,6-dichloro-1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole (4).

FIG. 7 shows an ¹H NMR spectra for1,3-bis(1-isoquinolylimino)-4,7-dihydroxyisoindole (5).

FIG. 8 shows an ¹H NMR and ¹³C NMR spectra for1,3-bis(2-pyridylimino)-4-ethoxy-7-hydroxyisoindole (6).

FIG. 9 shows the absorption spectra of Compounds (1)-(6).

FIG. 10 shows the emission spectra of Compounds (1)-(6).

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a new class of ESIPT dye molecules basedon mono or dihydroxy substituted 1,3-bisiminoisoindole motif. Theinvention is based, at least in part, on the discovery that mono ordihydroxy substituted BPI exhibits several of the characteristics commonto excited state intramolecular charge transfer (ESIPT) molecules. TheESIPT nature of such a compound was confirmed by both the lack ofemission from the alkoxy substituted BPI and the large changes inlifetime/efficiency in deuterated methanol (MeOD). Although ESIPTemission has been observed for similar compounds (IE hydroxyphthalimidebased ESIPT dyes), as described in Wakita, J.; Inoue, S.; Kawanishi, N.;Ando, S. Macromolecules 2010, 43 (8), 3594-3605, Sultanova, Nina;Staneva, T. Proc. Of SPIE 2003, 5226, 99-103, Gruzinsky, V. V.; andStaneva, T. G. Zh. Prikl. Spektr. 1975, 23 (5), 820-827, all of whichare incorporated herein by reference; the mono or dihydroxy substituted1,3-bisiminoisoindole motif in the compound of the invention offers oneimportant advantage, two readily modifiable substitutents not present inphthalimide.

In one embodiment, the invention provides a compound of the followingformula (I):

wherein Y₁ and Y₃ are independently S, O, or NR₁, and S, O, or NR₃,respectively, with at least one of Y₁ and Y₃ being NR₁ and NR₃,respectively, R₁ and R₃ each being an atom or a functional group,wherein R₁ and R₃ can optionally form a ring; R₂ is an atom or afunctional group, wherein R₂ can optionally form a ring with Y₁ and/orform a ring with Y₃; and X₁, X₂, and X₃ are independently N or CR₄, N orCR₅, and N or CR₆, respectively, R₄, R₅, and R₆ each being an atom or afunctional group, wherein R₄ and R₅ and/or R₅ and R₆ can optionally forma ring or R₄ and R₆ can optionally form a ring.

Typically, R₁, R₂, and R₃ are independently selected from the groupconsisting of H, a halogen, a hydroxy group, an amino group, a carboxylgroup, an aliphatic group, a heteroaliphatic group, a cyclic group, aheterocyclic group, an aromatic group, a heteroaromatic group, and acombination thereof. The combination includes, but not limited to, analiphatic aromatic group, an aliphatic heteroaromatic group; analiphatic cyclic group, and an aliphatic heterocyclic group. Theheteroaliphatic group includes, but not limited to, an aliphatic amine,an aliphatic acid, an aliphatic ketone, an aliphatic alkoxy, and analiphatic ester. In one embodiment, R₁, R₂, and/or R₃ is an alkyl,cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, or aralkyl.

Typically, R₄, R₅, and R₆ are independently selected from the groupconsisting of H, a halogen, a hydroxy group, an amino group, a carboxylgroup, an aliphatic group, a heteroaliphatic group, a cyclic group, aheterocyclic group, an aromatic group, a heteroaromatic group, and acombination thereof. The combination includes, but not limited to, analiphatic aromatic group, an aliphatic heteroaromatic group; analiphatic cyclic group, and an aliphatic heterocyclic group. Theheteroaliphatic group includes, but not limited to, an aliphatic amine,an aliphatic acid, an aliphatic ketone, an aliphatic alkoxy, and analiphatic ester. In one embodiment, R₄, R₅, and/or R₆ is an alkyl,cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, or aralkyl.

In a preferred embodiment, the invention provides dye molecules as shownin Scheme 2 below.

The compounds of the invention can be categorized according to thelocation of substitution. Below is a list of some categories containinga brief summary and several examples of each.

In one embodiment, Y₁ is NR₁. In another embodiment, Y₃ is NR₃. In stillanother embodiment, Y₁ is NR₁ and Y₃ is NR₃. R₁, R₂, and R₃ can be anyatom (including H) or group. Additionally, R₁, R₂, and R₃ can all be thesame or different groups depending on the synthetic method used.Examples of possible hydrocarbon groups at R₁, R₂, or R₃ are shown inScheme 3. Examples of other possible groups are shown in Scheme 4.

In addition to the possible independent substituents at R₁, R₂ and R₃,connections at R₁ and R₂, R₂ and R₃, and R₁ and R₃ are possible. Thus,in one embodiment, R₂ and R₃ together form a ring. In anotherembodiment, R₁ and R₂ together form a ring. In still another embodiment,R₁ and R₃ together form a ring. This category also contains anymolecules with extended conjugation at position R₁ and R₂ and/or R₂ andR₃. Any of the extended moieties can be added at R₁ and R₂ and/or R₂ andR₃. In another embodiment, rings formed at both R₁ and R₂ and R₂ and R₃and fused together.

In one embodiment, R₂ and R₃ or R₁ and R₂ together form a six memberedring bridging R₂ and R₃ or R₁ and R₂ with —CH═CH—. In a preferredembodiment, R₁ and R₂ or R₂ and R₃ together form a ring selected fromthe group consisting of phenylene, naphthalene, anthracene, andheterocyclic analogs of the same.

Examples of this type of structure are shown in Scheme 5.

In another embodiment, the invention provides a compound of thefollowing formula:

This is an example of the compound wherein R₂ and R₃ together form aring.

In another embodiment, the invention provides a compound of thefollowing formula:

This is an example of the compound wherein R₁ and R₂ together form aring.

R₄, R₅, and R₆ can be any atom (including H) or group. Additionally,R₄₋₆ can all be the same or different groups. In a preferred embodiment,X₃ is CR₆, where R₆ is a hydroxy group. In another embodiment, X₁ isCR₄, X₂ is CR₅, and X₃ is CR₆.

In one embodiment, R₄ and R₅ together form a ring or R₅ and R₆ togetherform a ring. In another embodiment, R₄ and R₆ together form a ring. Thiscategory also contains any molecules with extended conjugation atposition R₄ and R₅ and/or R₅ and R₆. Any of the extended moieties can beadded at R₄ and R₅ and/or R₅ and R₆. In another embodiment, rings formedat both R₄ and R₅ and R₅ and R₆ and fused together. Examples of thesecompounds are shown in Scheme 6.

In another embodiment, R₄ and R₅ or R₅ and R₆ together form a sixmembered ring bridging R₄ and R₅ or R₅ and R₆ with —CH═CH—. In apreferred embodiment, R₄ and R₅ or R₅ and R₆ together form a ringselected from the group consisting of phenylene, naphthalene,anthracene, and heterocyclic analogs of the same.

In a specific embodiment, the invention provides a compound of formula(I) in which Y₁ and Y₃ are NR₁ and NR₃, respectively, R₁ and R₃ beingthe same functional group selected from the group consisting of C₁₂H₂₅,4-tBu-Ph, 2-pyridyl, and 1-isoquinolyl; R₂ is H; X₁ and X₂ are CR₄ andCR₅, respectively, R₄ and R₅ being OH or Cl, and X₃ is CR₆, R₆ being OHor OEt.

The invention also provides metal complexes containing any of theaforementioned compounds as ligands coordinated to a metal center(either transition metal or lanthanide). Preferably, the compoundcoordinates to the metal center as either a tridentate or bidentateligand. In a similar manner multiple ligands can be coordinated to asingle metal center. In one embodiment, the metal complex contains twoor more ligands, at least one of which is a compound of the invention.

In one embodiment, the invention provides a complex comprising a metalatom M and a ligand as shown by the following formula (II):

wherein - - - - - represents an optional coordination bond, preferablyat least one of which being present, and wherein Y₁ and Y₃ areindependently S, O, or NR₁, and S, O, or NR₃, respectively, with atleast one of Y₁ and Y₃ being NR₁ and NR₃, respectively, R₁ and R₃ eachbeing an atom or a functional group, at least one containing an atom forforming a coordination bond, wherein R₁ and R₃ can optionally form aring; and X₁, X₂, and X₃ are independently N or CR₄, N or CR₅, and N orCR₆, respectively, R₄, R₅, and R₆ each being an atom or a functionalgroup, wherein R₄ and R₅ and/or R₅ and R₆ can optionally form a ring orR₄ and R₆ can optionally form a ring.

In one embodiment, Y₃ is NR₃, where R₃ is a functional group containingan atom for forming a coordination bond. In another embodiment, Y₁ isNR₁, where R₁ is a functional group containing an atom for forming acoordination bond. In still another embodiment, R₁ and/or R₃ is afunctional group comprising a nitrogen which forms a coordination bondwith M.

The metal M can be a transition metal or a lanthanide. In oneembodiment, M is a third row transition metal. In a specific embodiment,M is Ir, Pt, Re, or Os. In another embodiment, M is a second rowtransition metal. In a specific embodiment, M is Pd, Rh, or Ru. Inanother specific embodiment, M is La, Ce, Nd, or Eu.

In a specific embodiment, Y₁ and Y₃ are NR₁ and NR₃, respectively, R₁and R₃ being the same functional group selected from the groupconsisting of 2-pyridyl, and 1-isoquinolyl; X₁ and X₂ are CR₄ and CR₅,respectively, R₄ and R₅ being OH or Cl, and X₃ is CR₆, R₆ being OH orOEt.

In one embodiment, the invention provides the following metal complexescontaining an ESIPT molecule of the invention as a ligand.

wherein

represents an optional ring, L represents a ligand, where m and nrepresent the number of respective ligands, e.g., m=1, 2, 3, 4, 5, 6, ormore, and n=1, 2, 3, 4, or more.

The compounds of the invention with readily variable structure can besynthesized by any method known in the art. The photophysical propertiesof the compounds of the invention can be tuned through substitution. Thecompounds exhibit relatively high efficiencies (Φ>0.20) and molarabsorptivities (ε>1×10⁴ M⁻¹ cm⁻¹), making these dyes ideal candidatesfor many applications including, but not limited to, laser dyes (see,e.g., Chou, P.; McMorrow, D.; Aartsma, T. J.; Kasha, M. J. Phys. Chem.1984, 88, 4596-4599), fluorescent probes (see, e.g., Sytnik, A.; DelValle, J. C. J. Phys. Chem. 1995, 99, 13028-13032), photostabilizers(see, e.g., Chou, P. T.; Martinez, M. L. Radiat. Phys. Chem. 1993, 41,373-378), and high energy radiation detectors (see, e.g., Stein, M.;Keck, J.; Waiblinger, F.; Fluegge, A. P.; Kramer, H. E. A.; Hartschuh,A.; Port, H.; Leppard, D.; Rytz, G. J. Phys. Chem. A, 2002, 106,2055-2066), all of which are incorporated herein by reference.

In one embodiment, the invention provides an OLED containing thecompound and/or the metal complex of the invention as the emissivematerial. The compound and/or the metal complex of the invention can beincluded in one or more emissive layers of the OLED. In one embodiment,the compound and/or the metal complex of the invention is included inthe emissive layer as a dopant in a host material, e.g., a host materialdisclosed hereinbelow. In another embodiment, the compound and/or themetal complex of the invention is used in an OLED in combination with aphosphorescent material, e.g., a phosphorescent material disclosedhereinbelow.

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “excition”, which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference. The compound and/or the metal complex of the invention canbe used in OLEDs in combination with a phosphorescent material, e.g., inthe same emissive layer or in separate emissive layers.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F₄-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink-jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18° C. to 30° C., and morepreferably at room temperature (20-25° C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined below.

The term “halo” or “halogen” as used herein includes fluorine, chlorine,bromine and iodine.

The term “alkyl” as used herein contemplates both straight and branchedchain alkyl radicals. Preferred alkyl groups are those containing fromone to fifteen carbon atoms and includes methyl, ethyl, propyl,isopropyl, butyl, isobutyl, tert-butyl, and the like. Additionally, thealkyl group may be optionally substituted with one or more substituentsselected from halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR,wherein each R is independently selected from H, alkyl, alkenyl,alkynyl, aralkyl, aryl and heteroaryl.

The term “cycloalkyl” as used herein contemplates cyclic alkyl radicals.Preferred cycloalkyl groups are those containing 3 to 7 carbon atoms andincludes cyclopropyl, cyclopentyl, cyclohexyl, and the like.Additionally, the cycloalkyl group may be optionally substituted withone or more substituents selected from halo, CN, CO₂R, C(O)R, NR₂,cyclic-amino, NO₂, and OR.

The term “alkenyl” as used herein contemplates both straight andbranched chain alkene radicals. Preferred alkenyl groups are thosecontaining two to fifteen carbon atoms. Additionally, the alkenyl groupmay be optionally substituted with one or more substituents selectedfrom halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR.

The term “alkynyl” as used herein contemplates both straight andbranched chain alkyne radicals. Preferred alkyl groups are thosecontaining two to fifteen carbon atoms.

Additionally, the alkynyl group may be optionally substituted with oneor more substituents selected from halo, CN, CO₂R, C(O)R, NR₂,cyclic-amino, NO₂, and OR.

The terms “aralkyl” as used herein contemplates an alkyl group that hasas a substituent an aromatic group. Additionally, the aralkyl group maybe optionally substituted on the aryl with one or more substituentsselected from halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR.

The term “heterocyclic group” as used herein contemplates non-aromaticcyclic radicals. Preferred heterocyclic groups are those containing 3 or7 ring atoms which includes at least one hetero atom, and includescyclic amines such as morpholino, piperdino, pyrrolidino, and the like,and cyclic ethers, such as tetrahydrofuran, tetrahydropyran, and thelike. Additionally, the heterocyclic group may be optionally substitutedwith one or more substituents selected from halo, CN, CO₂R, C(O)R, NR₂,cyclic-amino, NO₂, and OR.

The term “aryl” or “aromatic group” as used herein contemplatessingle-ring groups and polycyclic ring systems. The polycyclic rings mayhave two or more rings in which two carbons are common by two adjoiningrings (the rings are “fused”) wherein at least one of the rings isaromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryl,heterocycles and/or heteroaryls. Additionally, the aryl group may beoptionally substituted with one or more substituents selected from halo,CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR.

The term “heteroaryl” as used herein contemplates single-ringhetero-aromatic groups that may include from one to three heteroatoms,for example, pyrrole, furan, thiophene, imidazole, oxazole, thiazole,triazole, pyrazole, pyridine, pyrazine and pyrimidine, and the like. Theterm heteroaryl also includes polycyclic hetero-aromatic systems havingtwo or more rings in which two atoms are common to two adjoining rings(the rings are “fused”) wherein at least one of the rings is aheteroaryl, e.g., the other rings can be cycloalkyls, cycloalkenyls,aryl, heterocycles and/or heteroaryls. Additionally, the heteroarylgroup may be optionally substituted with one or more substituentsselected from halo, CN, CO₂R, C(O)R, NR₂, cyclic-amino, NO₂, and OR.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table 1below. Table 1 lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

TABLE 1 MATE- PUBLI- RIAL EXAMPLES OF MATERIAL CATIONS Hole injectionmaterials Phthalo- cyanine and porphryin com- pounds

Appl. Phys. Lett. 69, 2160 (1996) Starburst triaryl- amines

J. Lumin. 72-74, 985 (1997) CF_(x) Fluoro- hydro- carbon polymer

Appl. Phys. Lett. 78, 673 (2001) Con- ducting polymers (e. g., PEDOT:PSS, poly- aniline, poly- pthio- phene)

Synth. Met. 87, 171 (1997) Aryl- amines com- plexed with metal oxidessuch as molyb- denum and tungsten oxides

SID Symposium Digest, 37, 923 (2006) Hole transporting materialsTriaryl- amines (e. g., TPD, α-NPD)

Appl. Phys. Lett. 51, 913 (1987)

US5061569

EP650955

J. Mater. Chem. 3, 319 (1993)

Appl. Phys. Lett. 90, 183503 (2007)

Appl. Phys. Lett. 90, 183503 (2007) Triaryl- amine on spiro- fluorenecore

Synth. Met. 91, 209 (1997) Aryl- amine carbozle com- pounds

Adv. Mater. 6, 677 (1994) Indolo- carba- zoles

Synth. Met. 111, 421 (2000) Isoindole com- pounds

Chem. Mater. 15, 3148 (2003) Phosphorescent OLED host materials Redhosts Aryl- carba- zoles

Appl. Phys. Lett. 78, 1622 (2001) Metal 8- hydroxy- quino- lates (e. g.,Alq₃, BAlq)

Nature 395, 151 (1998)

US20060202194

WO2005014551 Metal phenoxy- benzo- thiazole com- pounds

Appl. Phys. Lett. 90, 123509 (2007) Conju- gated oligo- mers and poly-mers (e. g., poly- fluorene)

Org. Electron. 1, 15 (2000) Green hosts Aryl- carba- zoles

Appl. Phys. Lett. 78, 1622 (2001)

US2003175553

WO2001039234 Aryltri- phenylene com- pounds

US20060280965

US20060280965 Poly- mers (e.g., PVK)

Appl. Phys. Lett. 77, 2280 (2000) Spiro- fluorene com- pounds

WO2004093207 Metal phenoxy- benzo- oxazole com- pounds

WO05089025

WO06132173

JP200511610 Spiro- fluorene- carbazole com- pounds

JP2007254297

JP2007254297 Idolo- cabazoles

WO07063796

WO07063754 5- member ring electron deficient hetero- cycles (e. g.,triazole, oxa- diazole)

J. Appl. Phys. 90, 5048 (2001)

WO04107822 Metal phenoxy- pyridine com- pounds

WO05030900 Blue hosts Aryl- carba- zoles

Appl. Phys. Lett. 82, 2422 (2003)

US20070190359 Dibenzo- thiophene- carbazole com- pounds

WO2006114966 Phosphorescent dopants Red dopants Heavy metal porphyrins(e. g., PtOEP)

Nature 395, 151 (1998) Iridium (III) organo- metallic com- plexes

Appl. Phys. Lett. 78, 1622 (2001)

US06835469

US06835469

US20060202194

US20060202194

US07087321

US07087321

Adv. Mater. 19, 739 (2007) Platinum (II) organo- metallic com- plexes

WO2003040257 Osminum (III) com- plexes

Chem. Mater. 17, 3532 (2005) Ruthe- nium (II) com- plexes

Adv. Mater. 17, 1059 (2005) Green dopants Iridium (III) organo- metalliccom- plexes

Inorg. Chem. 40, 1704 (2001)

US2002034656

US06687266

Chem. Mater. 16, 2480 (2004)

US2007190359

US 2006008670 JP2007123392

Adv. Mater. 16, 2003 (2004)

Angew. Chem. Int. Ed. 2006, 45, 7800 Pt(II) organo- metallic com- plexes

Appl. Phys. Lett. 86, 153505 (2005)

Appl. Phys. Lett. 86, 153505 (2005)

Chem. Lett. 34, 592 (2005) Gold com- plexes

Chem. Commun. 2906 (2005) Rhenium (III) com- plexes

Inorg. Chem. 42, 1248 (2003) Blue dopants Iridium (III) organo- metalliccom- plexes

WO2002002714

WO2006009024

US2006251923

WO2006056418, US2005260441

US2007190359

US2002134984

Angew. Chem. Int. Ed. 47, 1 (2008)

Chem. Mater. 18, 5119 (2006)

Inorg. Chem. 46, 4308 (2007)

WO05123873

WO05123873

WO07004380

WO06082742 Osmium (II) com- plexes

US2005260449

Organo- metallics 23, 3745 (2004) Gold com- plexes

Appl. Phys. Lett. 74, 1361 (1999) Platinum (II) com- plexes

WO06098120, WO06103874 Exciton/hole blocking layer materials Bathocu-prine com- pounds (e. g., BCP, BPhen)

Appl. Phys. Lett. 75, 4 (1999)

Appl. Phys. Lett. 79, 449 (2001) Metal 8- hydroxy- quinolates (e. g.,BAlq)

Appl. Phys. Lett. 81, 162 (2002) 5- member ring electron deficienthetero- cycles such as triazole, oxa- diazole, imi- dazole, benzo- imi-dazole

Appl. Phys. Lett. 81, 162 (2002) Tri- phenylene com- pounds

US20050025993 Fluor- inated aromatic com- pounds

Appl. Phys. Lett. 79, 156 (2001) Electron transporting materials Anthra-cene- benzo- imi- dazole com- pounds

WO03060956 Anthra- cene- benzo- thiazole com- pounds

Appl. Phys. Lett. 89, 063504 (2006) Metal 8- hydroxy- quino- lates (e.g., Alq₃)

Appl. Phys. Lett. 51, 913 (1987) Metal hydroxy- beno- quino- lates

Chem. Lett. 5, 905 (1993) Bathocu- prine com- pounds such as BCP, BPhen,etc

Appl. Phys. Lett. 91, 263503 (2007)

Appl. Phys. Lett. 79, 449 (2001) 5- member ring electron deficienthetero- cycles (e. g., triazole, oxa- diazole, imi- dazole, benzo- imi-dazole)

Appl. Phys. Lett. 74, 865 (1999)

Appl. Phys. Lett. 55, 1489 (1989)

Jpn. J. Apply. Phys. 32, L917 (1993) Silole com- pounds

Org. Electron. 4, 113 (2003) Aryl- borane com- pounds

J. Am. Chem. Soc. 120, 9714 (1998) Fluor- inated aromatic com- pounds

J. Am. Chem. Soc. 122, 1832 (2000)

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore includes variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

EXAMPLES Synthesis of Example Compounds

The compounds listed in Table 2 were synthesized with the same generalprocedure as previously reported for unsubstituted BPI (Scheme 1) asdescribed in Siegl, W. O. J. Org. Chem. 1977, 42, 1872-1878, Baird, D.M.; Maehlmann, W. P.; Bereman, R. D.; Singh, P. J. Coord. Chem. 1997,42, 107-126, all of which are incorporated by reference.

TABLE 2 The structure of alcohol/ethoxy substituted 1,3-bis(aryl oralkyl)isoindoline dyes.

Complex R1 R2 R3 R4 1 —C₁₂H₂₅ H OH OH 2 (4-tBu-Ph) H OH OH 3 2-Pyridyl HOH OH 4 2-Pyridyl Cl OH OH 5 1-isoquinolyl H OH OH 6 2-Pyridyl H OEt OH

The general synthesis goes as follows: 1 equivalent dicyano species, 2.1equivalents aryl or alkylamine and 0.1 equivalents CaCl₂ were refluxedin butanol or hexanol under N₂. After the reaction was discontinued thesolvent was either removed by distillation or the reaction mixturepoured into water and the precipitate was collected by filtration. Afterwashing with water, the products were then isolated by either columnchromatography or precipitation from boiling solvent followed byrecrystallization to give the desired products.

1,3-bis(dodecylimino)-4,7-dihydroxyisoindole (1)

A solution of 1.00 g 1,2-dicyanohydroquinone (6.24 mmol), 2.43 gdodecylamine (13.11 mmol) and 0.14 g CaCl₂ (1.3 mmol) in 30 ml 1-butanolwas refluxed under N₂ for 5 days. The reaction mixture was poured into500 mL of H₂O. The precipitate was collected by filtration and waswashed with water until no blue fluorescents was observed from thefiltrate. The precipitate was then dissolved in boiling methanol andthen cooled to 0° C. for 3 days. Precipitate was then collected byfiltration and washed with MeOH. 1.1 g (34%), orange solid. Product wasfurther purified by dissolving in CH₂Cl₂ and layering with MeOH. MS(Maldi-TOF): m/z=513.91. HRMS-FAB (m/z): [M+H]⁺ calcd for C₃₂H₅₆N₃O₂,514.4367; found, 514.4376. ¹H NMR (400 MHz, CDCl₃, δ) 6.70 (s, 2H), 3.69(t, J=6.4 Hz, 4H), 1.76-1.64 (m, 4H), 1.49-1.05 (m, 36H), 0.86 (t, J=6.4Hz, 6H). ¹³C NMR (100 MHz, CDCl₃, δ) 173.5, 155.2, 128.5, 113.3, 50.8,43.3, 31.9, 29.64, 29.62, 29.60, 29.5, 29.3, 29.2, 26.7, 22.7, 14.1.

1,3-bis(p-tert-butyl-phenylimino)-4,7-dihydroxyisoindole (2)

A solution of 1.00 g 1,2-dicyanohydroquinone (6.24 mmol), 2.09 mlp-tert-butyl-analine (13.11 mmol) and 66 mg CaCl₂ (0.62 mmol) in 10 ml1-hexanol was refluxed under N₂ for 2 days. The solvent was removedunder reduced pressure and the residue was washed with water. Theremaining solid dissolved in methanol and loaded onto silica gel byrotary evaporation. The product was then dry loaded onto a silica gelcolumn and product separated by first eluting with CH₂Cl₂ then a 100:1mixture of CH₂Cl₂ and Methanol. The emissive orange fraction wascollected and rotary evaporated to dryness. The residue was thendissolved in hot methanol and cooled to −40° C. for two days. Theprecipitate was collected by filtration. 152 mg (6%), purple powder. MS(Maldi-TOF): m/z=441.75. HRMS-FAB (m/z): [M+H]⁺ calcd for C₂₈H₃₂N₃O₂,442.2489; found, 442.2483. ¹H NMR (500 MHz, CDCl₃, δ) 7.66 (s, 1H), 7.39(d, J=7.5 Hz, 4H), 7.02 (d, J=7.5 Hz, 4H), 7.00 (s, 2H), 1.31 (s, 18H).

1,3-bis(2-pyridylimino)-4,7-dihydroxy isoindole (3)

A solution of 1.0 g (6.24 mmol) 2,3-dicyanohydroquinone, 1.23 g (13.11mmol) 2-aminopyridine and 0.14 g (1.3 mmol) CaCl₂ in 20 ml 1-butanol wasrefluxed under N₂. Despite the presents of fluorescent blue2,3-dicyanohydroquinone starting material, as observed by TLC (CH₂Cl₂),the reaction was discontinued after 20 days. The reaction mixture waspoured into 500 mL of H₂O. The precipitate was collected by filtrationand was washed with water until no blue fluorescents was observed fromthe filtrate. The precipitate was then dissolved in boiling CH₂Cl₂ andthen cooled to −40° C. overnight. Precipitate was then collected byfiltration and washed with MeOH. 0.485 g (24%), yellow needles. MS(Maldi-TOF): m/z=331.85. HRMS-FAB (m/z): [M+H]⁺ calcd for C₁₈H₁₄N₅O₂,332.1142; found, 332.1136. ¹H NMR (400 MHz, CDCl₃), δ 13.3 (s, 1H), 8.57(ddd, J=4.8, 2.0, 0.8 Hz, 2H), 7.75 (ddd, J=8.0, 7.6, 2.0 Hz, 2H), 7.35(d, J=8.0 Hz, 2H), 7.11 (ddd, J=7.6, 4.8, 0.8 Hz, 2H), 7.00 (s, 2H). ¹³CNMR (100 MHz, CDCl₃) δ 159.3, 154.9, 149.0, 147.9, 147.9, 138.1, 122.4,121.4, 120.4, 116.2.

5,6-dichloro-1,3-bis(2-pyridylimino)-4,7-dihydroxyisoindole (4)

A solution of 800 mg (3.5 mmol)2,3-dichloro-5,6-dicyano-1,4-hydroquinone, 690 mg (7.34 mmol)2-aminopyridine and 78 mg (0.73 mmol) CaCl₂ in 15 ml of 1-hexanol wasrefluxed under N₂ for 2 days. The solvent was removed under reducedpressure. The residue was washed with water until no blue fluorescentswas observed from the filtrate. The remaining solid was dissolved inrefluxing CH₂Cl₂ and filtered while hot. The filtrate was then cooled to0° C. for 2 days. 254 mg (18%), black needles. MS (Maldi-TOF):m/z=400.06. HRMS-FAB (m/z): [M+H]⁺ calcd for C₁₈H₁₂Cl₂N₅O₂, 400.0363;found, 400.0354. ¹H NMR (400 MHz, CDCl₃), δ 8.55 (d, J=4.8 Hz, 2H), 7.81(t, J=7.6 Hz, 2H), 7.32 (d, J=7.6 Hz, 2H), 7.18 (t, J=5.6 Hz, 2H).

1,3-bis(1-isoquinolylimino)-4,7-dihydroxyisoindole (5)

A solution of 160 mg (1.0 mmol) 2,3-dicyanohydroquinone, 300 mg (2.08mmol) 1-aminopyridine and 78 mg (0.73 mmol) CaCl₂ in 15 ml of 1-hexanolwas refluxed under N₂ for 2 days. The solvent was removed under reducedpressure. The residue was washed with water until no blue fluorescentswas observed from the filtrate. The remaining solid was dissolved inrefluxing CH₂Cl₂ and filtered while hot. The filtrate was then cooled to−40° C. for 2 days. 64 mg (15%), green crystalline powder. MS(Maldi-TOF): m/z=431.63. HRMS-FAB (m/z): [M+H]⁺ calcd for C₂₆H₁₈N₅O₂,432.1455; found, 432.1446. ¹H NMR (400 MHz, CDCl₃), δ 8.62 (d, J=8.4,2H), 8.53 (d, J=6.0, 2H), 7.84 (d, J=8.4, 2H), 7.75 (t, J=6.8, 2H), 7.68(t, J=6.8, 2H), 7.53 (d, J=6.0, 2H), 7.10 (s, 2H).

1,3-bis(2-pyridylimino)-4-ethoxy-7-hydroxyisoindole (6)

A solution of 1.17 g (5.43 mmol) 3,6-diethoxyphthalonitrile, 1.28 g(13.6 mmol) 2-aminopyridine and 0.117 g (1.03 mmol) CaCl₂ in 17 ml1-hexanol was refluxed under N₂ and monitored for the disappearance of3,6-diethoxyphthalonitrile by TLC. Upon cooling to room temperature, thesolution was poured into 1 L of water and the product was extractedusing CH₂Cl₂. The organic layer was reduced in volume (50 ml) and thesolution was then rotary evaporated onto a silica gel. A silica gelcolumn was then dry loaded with the residue coated silica gel.Fluorescent blue 3,6-diethoxyphthalonitrile starting material wasobtained by first eluting with CH₂Cl₂. The desired product (fluorescentorange band) was then collected by eluting with CH₂Cl₂:MeOH (100:1).Solvent was removed by rotary evaporation and the residue was thendissolved in hot methanol and cooled to 0° C. The precipitate was thencollected by filtration. 0.140 g (7%), yellow needles. MS (Maldi-TOF):m/z=360.20. HRMS-FAB (m/z): [M+H]⁺ calcd for C₂₀H₁₈N₅O₂, 360.1455;found, 360.1452. ¹H NMR (400 MHz, CDCl₃), δ 13.8 (s, 1H), 8.60-8.55 (m,2H), 7.77-7.70 (m, 2H), 7.48 (d, J=8.0, 1H), 7.33 (d, J=8.0, 1H),7.13-7.06 (m, 2H), 7.05 (s, 1H), 7.04 (s, 1H), 4.28 (q, J=6.8, 2H), 1.55(t, J=6.8, 3H). ¹³C NMR (100 MHz, CDCl₃) δ 160.4, 159.3, 155.4, 153.0,150.4, 149.5, 148.0, 147.5, 138.0, 137.9, 124.1, 122.1, 121.0, 120.6,120.3, 120.1, 118.8, 66.1, 14.9. Elemental analysis for C₂₀H₁₈N₅O₂:calcd: C, 66.84, H, 4.77, N, 19.49. found: C, 67.16, H, 4.65, N, 19.08.

Absorption Properties of Example Compounds

The absorption spectra of compounds (1)-(6) are shown in FIG. 9 and themolar absorptivities are summarized in Table 3 below.

TABLE 3 Absorption maxima and molar absorptivity of compounds (1)-(6) intoluene, CH₂Cl₂ and methanol Mol- absorbance λ (nm) (ε, ×10⁴M⁻¹cm⁻¹)ecule Toluene CH₂Cl₂ MeOH 1 336(0.24), 499(0.84) 347(0.36), 492(0.97)345(0.34), 472(0.85) 2 379(1.71) 375(1.76) 384(1.05), 549(0.74),574(0.56), 593(0.43) 3 370(1.70), 388(2.00), 369(2.06), 387(2.40),366(1.68), 413(1.59), 437(1.09) 413(1.84), 431(1.22) 384(1.92),408(1.56), 543(0.07), 587(0.07) 4 401(1.56), 423(2.01), 363(1.29),478(0.31), 372(2.32), 448(1.54), 436(1.31), 514(0.97), 554(2.18),392(2.63), 516(0.07), 555(0.11), 599(2.87) 417(1.96), 603(0.09)517(0.56), 555(1.04), 601(1.04) 5 330(0.86), 344(0.65), 329(0.77),343(0.62), — 413(2.97), 436(3.31), 412(2.93), 434(3.14), 464(2.09)462(1.92) 6 371(2.36), 391(2.89), 371(2.82), 390(3.34), 367(1.83),414(2.20) 411(2.55) 386(2.11), 410(1.62)Emissive Properties of Example Compounds

The emission spectra of compounds (1)-(6) are shown in FIG. 10 and thedata are summarized in Table 4 below.

TABLE 4 Photophysical properties of compounds (1)-(6) in varioussolvents and PMMA. emission at 77 K^(a) emission at rt λ_(max) ComplexSolvent λ_(max) (nm) τ (ns) Φ_(PL) (nm) τ (ns) 1 MeOH 471, 549 6.99,8.39 0.482 474 8.84 CH₂Cl₂ 469, 567 6.84, 7.89 0.061 Toluene 575 7.340.049 PMMA 554 7.46 0.007 2 MeOH 600 4.14 0.121 625 4.7  CH₂Cl₂ 604 3.710.023 Toluene 590 3.05 0.040 PMMA 624 3.39 0.010 3 MeOH 592 3.67 0.305598 5.11 MeOD 593 6.69 0.690 CH₂Cl₂ 597 3.95 0.401 Toluene 602 3.290.366 PMMA 593 3.56 0.25 4 MeOH 613 4.15 0.254 622 5.99 CH₂Cl₂ 612 4.640.392 Toluene 614 3.64 0.346 5 MeOH 612, 662 0.844, 3.97 0.036 624 5.78,3.15 CH₂Cl₂ 612, 676 0.907, 3.30 0.029 Toluene 620, 670 0.882, 2.670.044 6 MeOH 600 3.8  0.293 620 5.27 CH₂Cl₂ 615 4.64 0.387 Toluene 6224.06 0.344 PMMA 616 4.36 0.292 ^(a)In 2-MeTHF. All samples recorded inPMMA were at 2% (w/w)

What is claimed is:
 1. A compound of the following formula:

wherein Y₁ is NR₁; or a compound of the following formula:

wherein Y₃ is NR₃, wherein X₁, X₂, and X₃ are independently N or CR₄, Nor CR₅, and N or CR₆, respectively, wherein R₄ and R₅ and/or R₅ and R₆can optionally form a ring or R₄ and R₆ can optionally form a ring,wherein R₁, R₃, R₄, R₅, and R₆ are independently selected from the groupconsisting of H, a halogen, a hydroxy group, an amino group, a carboxylgroup, an aliphatic group, a heteroaliphatic group, a cyclic group, aheterocyclic group, an aromatic group, a heteroaromatic group, and acombination thereof.
 2. A compound selected from the group consisting ofthe following compounds:

wherein X₁, X₂, and X₃ are independently N or CR₄, N or CR₅, and N orCR₆, respectively, wherein R₄ and R₅ and/or R₅ and R₆ can optionallyform a ring or R₄ and R₆ can optionally form a ring, wherein R₄, R₅, andR₆ are independently selected from the group consisting of H, a halogen,a hydroxy group, an amino group, a carboxyl group, an aliphatic group, aheteroaliphatic group, a cyclic group, a heterocyclic group, an aromaticgroup, a heteroaromatic group, and a combination thereof, wherein n canbe any number of repeating units.
 3. A complex comprising a metal atom Mand a ligand as shown by the following formula:

wherein - - - - - represents an optional coordination bond, at least oneof which being present, wherein Y₁ and Y₃ are NR₁ and NR₃, respectively,at least one containing an atom for forming a coordination bond, whereinR₁ and R₃ can optionally form a ring, wherein R₁ and R₃ are the samefunctional group selected from the group consisting of 2-pyridyl and1-isoquinolyl, wherein X₁ is CR₄, X₂ is CR₅, R₄ and R₅ being OH or Cl,and wherein X₃ is CR₆, R₆ being OH or OEt.